Residualidade e reaplicação de corretivo da acidez, associada ou não ao gesso, em Latossolo no Cerrado: alterações nos atributos químicos do solo no perfil e baixo impacto na produtividade da soja e do milho

Abstract

Soil reacidification is a slow process and starts from the surface. In soils under a no-tillage (NT) system the reacidification can be controlled by reapplying lime on the surface provided that the soil native potential acidity correction was done properly. There are still questions regarding the necessity to restart the NT when it was not adopted correctly. Gypsum is used to improve the soil environment for deep root growth due to its greater water solubility. Thus, the combined use of lime and gypsum can favor the correction of soil acidity and improve soil nutrient availability in deeper layers. The objective of the study was to evaluate the vertical nutrient distribution, soil acidity attributes changes, and crop yields due to reapplication strategies of soil acidity corrective and gypsum and verify the need to restart the NT system (with lime incorporation) to correct the soil reacidification process in an Oxisol of the Cerrado biome. The natural biome was converted into an agricultural system in 1983, and until 2008 the soil was constantly revolved and the application and reapplication of limestone were performed. The conversion of the conventional tillage to NT was done simply by stopping the soil tillage. Between 2008 and 2012, although cultivated with grain crops, no lime and plant nutrients were applied. In September 2012, six treatments were applied, following two strategies: i) maintenance of the NT system: without soil acidity corrective reapplication and no gypsum application (SC), superficial application of gypsum (GS), superficial reapplication of soil acidity corrective (CS), and superficial reapplication of soil acidity corrective associated with the superficial application of gypsum (CS + GS); and ii) restarting the NT system: soil acidity corrective incorporation (CI) and soil acidity corrective incorporation associated with the superficial application of gypsum (CI + GS). In September 2019, seven years after the installation of the experiment, the soil was sampled in eight stratified layers down to 50 cm deep (0-5, 5-10, 10-15, 15-20, 20-25, 25-30, 30-40 and 40-50 cm). The soil under the natural biome was also collected. The chemical attributes related to soil acidity, nutrient availability, and the yield of soybean (Glycine max L. Merril) and corn (Zea mays L.) were analyzed. The comparison of the attributes of soil acidity between the soil under natural biome and the soil under an agricultural system for 36 years without reapplication of soil acidity corrective for more than a decade shows that the soil reacidification process is slow. The superficial reapplication of lime reduced soil aluminum saturation down to 25 cm deep, without, however, its total neutralization and proved to be sufficient to maintain adequate levels of the attributes of soil acidity and nutrient availability. The incorporation of the soil acidity corrective changed the soil acidity attributes more homogeneously in the soil arable layer (i.e., 0-20 cm), with the effects been restricted to this layer. However, this strategy did not result in great benefits regarding the improvement of soil acidity attributes when compared to the superficial application of lime. The application of gypsum did not change aluminum dynamics in the soil profile, nor the crops yield. Soybean showed a positive yield response to the reapplication of the soil acidity corrective, regardless of the reapplication method (252 kg ha year-1 increase). Corn responded positively only when the lime was incorporated and associated with gypsum (578 kg ha year-1 increase) comparated with SC, but no difference was observed from the treatments that received lime. The losses caused by soil turning to incorporate the soil acidity corrective in a NT system are greater than the gains from corn yield increase. The losses caused by soil turning to incorporate the soil acidity corrective are greater than the gains from corn yield increase. There is no need to incorporate the soil acidity corrective once the soil native acidity was properly corrected, neither to apply gypsum to the soil under these conditions.